<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Interpret the metazoan phylogenetic tree
  • Describe the types of data that scientists use to construct and revise animal phylogeny
  • List some of the relationships within the modern phylogenetic tree that have been discovered as a result of modern molecular data

Biologists strive to understand the evolutionary history and relationships of members of the animal kingdom, and all of life, for that matter. The study of phylogeny aims to determine the evolutionary relationships between phyla. Currently, most biologists divide the animal kingdom into 35 to 40 phyla. Scientists develop phylogenetic trees, which serve as hypotheses about which species have evolved from which ancestors

Recall that until recently, only morphological characteristics and the fossil record were used to determine phylogenetic relationships among animals. Scientific understanding of the distinctions and hierarchies between anatomical characteristics provided much of this knowledge. Used alone, however, this information can be misleading. Morphological characteristics may evolve multiple times, and independently, through evolutionary history. Analogous characteristics may appear similar between animals, but their underlying evolution may be very different. With the advancement of molecular technologies, modern phylogenetics is now informed by genetic and molecular analyses, in addition to traditional morphological and fossil data. With a growing understanding of genetics, the animal evolutionary tree has changed substantially and continues to change as new DNA and RNA analyses are performed on additional animal species.

Constructing an animal phylogenetic tree

The current understanding of evolutionary relationships between animal, or Metazoa    , phyla begins with the distinction between “true” animals with true differentiated tissues, called Eumetazoa    , and animal phyla that do not have true differentiated tissues (such as the sponges), called Parazoa    . Both Parazoa and Eumetazoa evolved from a common ancestral organism that resembles the modern-day protists called choanoflagellates. These protist cells strongly resemble the sponge choanocyte cells today ( [link] ).

The image on the left shows a choanoflagellate, which is a single-celled protest. The image on the right shows a sponge choanocyte cell that lines in inside of a sponge. The two cells appear identical. Both are egg-shaped with a cone at the back end. A flagellum juts out from the wide part of the cone.
Cells of the protist choanoflagellate resemble sponge choanocyte cells. Beating of choanocyte flagella draws water through the sponge so that nutrients can be extracted and waste removed.

Eumetazoa are subdivided into radially symmetrical animals and bilaterally symmetrical animals, and are thus classified into clade Bilateria or Radiata, respectively. As mentioned earlier, the cnidarians and ctenophores are animal phyla with true radial symmetry. All other Eumetazoa are members of the Bilateria clade. The bilaterally symmetrical animals are further divided into deuterostomes (including chordates and echinoderms) and two distinct clades of protostomes (including ecdysozoans and lophotrochozoans) ( [link] ab). Ecdysozoa    includes nematodes and arthropods; they are so named for a commonly found characteristic among the group: exoskeletal molting (termed ecdysis). Lophotrochozoa    is named for two structural features, each common to certain phyla within the clade. Some lophotrochozoan phyla are characterized by a larval stage called trochophore larvae, and other phyla are characterized by the presence of a feeding structure called a lophophore.

Questions & Answers

what is body symmetry
Elizabeth Reply
What is the instrument used for measuring water potential?
Agyeiwaa Reply
tensiometers
osometer
MP
difference between food chain and food web
tunz Reply
is the study of living
Cabdi Reply
ohh ok..
HAMIDAH
hys
Cabdi
tro or right
Cabdi
yeah u re right, study of living
HAMIDAH
ok dear
Cabdi
aha
HAMIDAH
hee maxaa kwda hee
Cabdi
what is biology
Sandra Reply
Biology is the natural science that studies life n living organisms which include physical structures, chemical processes, molecular interaction, physiological mechanisms, evolution n development
HAMIDAH
biology is d study of living things
tunz
tru
Cabdi
brnch of biology
Cabdi
biology is the study of living things
tunz
hy hamidah
Cabdi
biology is the study of living things
Nikolas
main branch re botany, zoology n micro biology
HAMIDAH
1.Biochemistry 2.Biophysics 3.Biotechnology 4.Botany 5.Cell biology 6.Ecology
Peace
Main branch of biology are,zoology, botany and microbiology
Agyeiwaa
the period of cell growth between nuclear division
AAYAT Reply
what is synapsis
Edward Reply
the fusion of chromosomes at yhe the beginning of meiosis
Hassan
what do we mean by the team genetic
Regina Reply
is the inheritance of the living organisms
Sarah
am I right?
Sarah
is the variation and inheritance of living organism
Raymond
genetic is define as the scientific study of heredity and variation in living things
HAMIDAH
give all the characteristics of an enzyme
Davies Reply
it alters the rate of chemical reaction
tunz
-some require coenzymes -they re inhibited by inhibitors -they re required in minute amount -they speed up the rate of chemical reaction
HAMIDAH
hi Hamida, may I ask how do you study bio?
al
thanks
al
what is the difference between meiosi and
Glory Reply
TCRs. in full. and was it all about .Tell me about all of immunity.
KIIZA Reply
why is it that, when using light microscope for viewing the red blood cell is not distinguishable
Samuel Reply
Hello guy what is happening
Glory Reply
what is a cell
Innocent Reply
basic unit of life
Adoma
smallest unit of living things
Nicholas
cell is a basic unit of life
Senamile
the fundamental and structural unit of a living organism
angelina
what will happen if cytokenesis did not occurs during meiosi
Senamile Reply
hi
Samuel
The daughter cell would not separate from the parent cell.
Eric
it will separate when it matured
Oberdy
Really then what is the process
Samuel
what is a cell
Innocent
a cell is the basic unit of life
Samuel
what is the function if subcutaneous fat in the skin
Adoma
what is an endospermous seed
Glory
it served as a passageway for nerves and blood vessels between the skin and the muscle
Glory
that is for subcutaneous fat in the skin oo
Glory
Chromosomes are duplicated during what stage of cell cycle
Marsha
what are organic and inorganic fertilizer
Afia
the separation that exist between the parent cell and the daughter cell won't occur
Opoku

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask